Researchers have successfully produced baby rats from mice, confirming the theory that different animal species could become surrogate parents to one another.

Scientists have known since 1996 that stem cells from rat sperm inserted into mouse testicles can generate viable rat sperm.

Now Japanese scientists from Kyoto University have tested this theory by using a method called in vitro microinsemination.

This technique involves fertilizing rat eggs with mouse-grown rat sperm.

The rat sperm is then put in a Petri dish with rat eggs.

If all goes well, one or more of the rat eggs is fertilized by the rat sperm.

Finally, the rat eggs are inserted into the uterus of mice.

So far, this technique has produced 15 rats.

The scientists say that the use of small surrogate animals may be beneficial for future experiments involving larger animals, such as cattle.

The scientists say it’s possible to grow bull sperm in mice to help cattle producers save on space and food.

The rat/mouse study was published this week in the journal Proceedings of the National Academy of Sciences.